The drilling of wells for oil and gas production conventionally employs longitudinally extending sections or so-called “strings” of drill pipe to which, at one end, is secured a drill bit of a larger diameter. After a selected portion of the borehole has been drilled, the borehole is usually lined or cased with a string or section of casing or liner. Such a casing or liner exhibits a larger diameter than the drill pipe used to drill the borehole, and a smaller diameter than the drill bit. Conventionally, after the casing or liner string is placed in the borehole, the string is cemented into place.
Tubular strings, such as drill pipe, casing, or liner, may be surrounded by an annular space between the exterior wall of the pipe and the interior wall of the well casing or the borehole wall, for example. Frequently, it is desired to seal such an annular space between upper and lower portions of the well depth. The annular region may be sealed with a downhole article that seals the annular space, such as between a casing wall and a tubular component, such as a length of production tubing. Swellable packers are particularly useful for sealing an annular space because they swell (e.g., expand) upon exposure to wellbore fluids and fill the cross-sectional area of the annular space in response to contact with one or more downhole fluids. Such materials that swell upon exposure to a fluid without negatively affecting the properties of the material are referred to herein as “swellable materials.”
However, contaminants such as metallic cations within the wellbore fluid may negatively affect the operation of swellable materials. For example, cations within the wellbore fluid may increase the amount of time it takes for a swellable material to fully expand, may decrease the total amount of swelling of the swellable material, and may accelerate degradation of the swellable material.
In the subterranean hydrocarbon (i.e., oil and gas), as well as geothermal drilling and completion industries, fluids containing contaminants (referred to in the industry as flowback fluids) often may return to the surface. Because the flowback fluids contain contaminants, environmental regulations often require that the flowback fluids be treated before they are discharged or reused.
It would, therefore, be desirable to have improved methods of removing contaminants from both wellbore fluids and flowback fluids. It would also be desirable to have improved methods of forming a swellable downhole article for sealing an annular space within the interior of a wellbore in the presence of cations.